Reactions of aquacobalamin and cob(II)alamin with chlorite and chlorine dioxide.

Reactions of aquacobalamin (H2O-Cbl(III)) and its one-electron reduced form (cob(II)alamin, Cbl(II)) with chlorite (ClO2-) and chlorine dioxide (ClO 2• ) were studied by conventional and stopped-flow UV-Vis spectroscopies and matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS). ClO2- does not react with H2O-Cbl(III), but oxidizes Cbl(II) to H2O-Cbl(III) as a major product and corrin-modified species as minor products. The proposed mechanism of chlorite reduction involves formation of OCl- that modifies the corrin ring during the course of reaction with Cbl(II). H2O-Cbl(III) undergoes relatively slow destruction by ClO 2• via transient formation of oxygenated species, whereas reaction between Cbl(II) and ClO 2• proceeds extremely rapidly and leads to the oxidation of the Co(II)-center.